The freeze-fracture technique will be used to study the potential of synaptic membranes to respond to changes in the synaptic environment. This will be accomplished by studying the response of the postsynaptic membrane to: (1) deafferentation; (2) the transneuronal effects of deafferentation; and (3) axotomy. The changes in the postsynaptic membrane specializations of the principal neuron in the rostral anteroventral cochlear nucleus of the guinea pig will be studied under these three conditions. This study will be important for understanding the mechanisms involved in establishing and maintaining synaptic contacts. In addition, information will be gained concerning the roles that presynaptic and postsynaptic neurons play in maintaining the postsynaptic membrane specializations. Finally, the freeze-fracture technique will contribute new information concerning the response of a CNS neuron to pathological conditions. This research will also contribute significantly to the understanding of the auditory system. It will include an intensive thin section and freeze-fracture study of a single synapse of the spiral ganglion cells in the rostral AVCN. By studying the particle distribution on the postsynaptic membrane under different experimental conditions insight will be gained as to the relationship of the different particle specializations to synaptic function at the primary auditory synapse. Future work resulting from this study will focus on comparing the events that occur on the postsynaptic membrane during degeneration with that which occurs during the development of the synaptic contacts. Evidence on the development of receptors in the neuromuscular junction and of synaptic specializations during the synaptogenesis in tissue culture indicate that such comparisons would be significant. The characteristic size and arrangements of the end bulb of Held in the anterior AVCN make it easy to identify in thin sections and freeze-fracture replicas. These same features would make this synapse a good model for future studies on synaptic development with the freeze-fracture technique.